1. Field of the Invention
The invention provides nucleotide sequences from coryneform bacteria which code for malate dehydrogenase and a process for the fermentive preparation of amino acids using bacteria in which the mdhA gene is attenuated.
2. Discussion of the Background
L-Amino acids, in particular lysine, are used in human medicine, in pharmaceuticals, in foodstuffs and in animal nutrition.
It is known that amino acids are prepared by fermentation from strains of Coryneform bacteria, in particular Corynebacterium glutamicum. Because of their great importance, work is constantly being undertaken to improve the preparation processes. Improvements to the process can relate to fermentation measures, such as, for example, stirring and supply of oxygen, or the composition of the nutrient media, such as, for example, the sugar concentration during the fermentation, or the working up to the product form by, for example, ion exchange chromatography, or the intrinsic output properties of the microorganism itself.
Methods of mutagenesis, selection and mutant selection are used to improve the output properties of these microorganisms. Strains which are resistant to antimetabolites or are auxotrophic for metabolites of regulatory importance and which produce amino acids are obtained in this manner.
Methods of the recombinant DNA technique have also been employed for some years for improving the strain of Corynebacterium strains which produce L-amino acids.
However, there remains a critical need for improved methods of producing L-amino acids and thus for the provision of strains of bacteria producing higher amounts of L-amino acids. On a commercial or industrial scale even small improvements in the yield of L-amino acids, or the efficiency of their production, are economically significant. Prior to the present invention, it was not recognized that attenuation of the mdhA gene encoding a malate dehydrogenase would improve L-amino acid yields. Thus, the present inventors had the object of providing new methods for improved fermentative preparation of amino acids, in particular L-lysine.